Certain engineered plastics, such as styrene-maleic anhydride copolymers (SMA's) and high impact polystyrenes (HIPS), are prepared in the presence of a rubber, for example, a polybutadiene or a styrene-butadiene copolymer, to enhance toughness, impact strength and other properties. A low solution viscosity additive rubber can facilitate the dispersion of the rubber in the plastic phase. Moreover, early in polymerization of HIPS, phase separation begins because of the immiscibility of the rubber within the polystyrene being formed and depletion of the styrene phase. Furthermore, in SMAs, a low solution viscosity may improve the clarity and the gloss of the resultant product.
While low solution viscosity of the additive rubber is highly desirable, it makes commercial handling difficult. Moreover, low solution viscosity typically leads to a liquid or semi-liquid material that is difficult to package and ship. Accordingly, a relatively high bulk viscosity material capable of being baled into a shippable and easy to handle form is desirable.
Significant work has been conducted in the art of polymerizing vinyl compounds, particularly conjugated dienes. However, there has been no suggestion to use the present inventive polymerization technique for termination of the reaction to achieve a high bulk viscosity, low solution viscosity rubber compound.
The present invention uses CO2 termination of the polymerization process to yield a highly desirable product. Importantly, while the use of CO2 termination of polymerization has been utilized before, CO2 reaction termination has previously been performed to provide a reactive product by the immediate protonation or other activation of the polymeric material. For example, U.S. Pat. No. 3,070,579 teaches reacting a living polymer, i.e., a polymerizable chemo-aromatic hydrocarbon having reactive negatively charged end groups, with a compound such as a CO2, CS2, 1,2-propylene oxide or ethylene oxide while having the reactants dissolve in a liquid. The patent further states that because of the reactive end groups, the bifunctional polymeric product is reacted with other groups or compounds to form many compositions.
The present invention advantageously provides a low molecular weight carboxylated polymeric material having a bulk viscosity particularly suitable for addition to SMA or HIPS resins.